How to use the Parcelable class properly in Android

Question

I have a class (below) that I want to send to a Service Class through an Intent. I have implemented the Parcelable interface but am unsure how to actually send and retrieve the entire object including the current state of the object.

In particular

@Override 
public void writeToParcel(Parcel dest, int flags) {
      //I need this to send the entire state of the object
}

And

public UrlParamsHelper(Parcel in) {
    //I need this to unpack the state of the object
}

Here is the actual class

/*
  * A holder class for URL parameters
  */
 public static class UrlParamsHelper implements Parcelable {
  private final HttpClient httpClient;
  private final HttpParams params = new BasicHttpParams();
  private final SchemeRegistry registry = new SchemeRegistry();
  private final ThreadSafeClientConnManager manager;
  private final Uri.Builder uri = new Uri.Builder();
  final HttpHost host;

  final String urlPath;
  final String hostname;
  /*
   * @param hostname the hostname ie. http://www.google.com
   * @param urlPath the path to the file of interest ie. /getfiles.php
   */
  public  UrlParamsHelper(final String hostname, final String urlPath) {
   HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
   HttpProtocolParams.setContentCharset(params, "UTF-8");
   registry.register(new Scheme("http",PlainSocketFactory.getSocketFactory(), 80));
   manager = new ThreadSafeClientConnManager(params, registry);
   httpClient = new DefaultHttpClient(manager, params);
   host = new HttpHost(hostname, 80, "http");
   uri.path(urlPath);

   this.urlPath = urlPath;
   this.hostname = hostname;
  }

  public UrlParamsHelper(Parcel in) {
   //unpack the state
  }

  public void addQueryString(String key, String value) {
   uri.appendQueryParameter(key, value);
  }

  public HttpGet buildGetQuery() {
   return new HttpGet(uri.build().toString());
  }

  public HttpClient getHttpClient() {
   return httpClient;
  }

  public HttpHost getHttpHost() {
   return host;
  } 

  @Override
  public int describeContents() {
   return 0;
  }

  @Override
  public void writeToParcel(Parcel dest, int flags) {
   //Parcel the entire state of the object
  }

  //Constructs the parcel again - REQUIRED
      public static final Parcelable.Creator<UrlParamsHelper> CREATOR = new Parcelable.Creator<UrlParamsHelper>() {
       public UrlParamsHelper createFromParcel(Parcel in) {
           return new UrlParamsHelper(in);
       }

       public UrlParamsHelper[] newArray(int size) {
        throw new UnsupportedOperationException();
           //return new UrlParamsHelper[size];
       }
   };
 }

Answer 1

In your writeToParcel function, you need to write which state objects you want to the Parcel, for instance:

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(urlPath);
    dest.writeString(hostname);
}

It doesn't matter which order you write the objects, so long as you read them back in in the same order:

@Override
public UrlParamsHelper(Parcel in) {
    urlPath = in.readString();
    hostname = in.readString();
}

The problem is that you can only read and write the object types mentioned in the documentation for Parcel, so it may be difficult to save absolutely everything.